1. Field of the Invention
The present invention relates to optical disk reproducing systems, and more particularly, to an apparatus and method for generating an eight-to-fourteen modulation (EFM) signal in an optical disk reproducing system, in which a radio frequency (RF) signal is converted into the EFM signal.
2. Description of the Related Art
Optical disk reproducing systems relating to compact disk (CD) systems or digital video disk (DVD) systems pick up light reflected by an optical disk and convert the light into an RF signal. They then convert the RF signal into an EFM signal, and reproduce multi-media data stored in the disk using the EFM signal.
In the case where the optical disk has a defect, for example, a pin hole or pin depth defect, and is a wobble disk, i.e., a disk that is bent to such an extent that the RF signal vibrates, distortion exists in the RF signal itself, which is used to generate an EFM signal. Here, the term pin depth defect refers to a defect in which the depth of a pin hole defect in an optical disk is so deep that light cannot be reflected by the optical disk, resulting in failure in detection of an RF signal. The pin hole defect refers to when a hole, through which light passes, exists in the optical disk.
A conventional EFM signal detection apparatus which detects an EFM signal from a distorted RF signal when the RF signal is not accurately detected due to a defect of the disk such as that described above, using a level detection method or an envelope detection method. For example, a conventional EFM signal generating apparatus which slices an RF signal by receiving a digital sum value (DSV), which will be described later, has been disclosed by Philips Corporation, in an article entitled, xe2x80x9cData Slicer Showing Typical Application Components,xe2x80x9d Specification of SAA7372, p.10, 6 December 1995. A conventional EFM signal generating apparatus which generates an EFM signal by self-slicing an RF signal using a current type method, has been disclosed in a book by John Watkinson, entitled The art of Digital Audio (published by Focal Co., Inc.).
The above-mentioned conventional EFM signal detection apparatus using the level detection method corrects the asymmetry of an RF signal, generates a slice reference level using the asymmetry-corrected RF signal, and slices the RF signal based on the generated slice reference level, resulting in an EFM signal. Such a conventional EFM signal generating apparatus is suitable for compensating for distortion of an RF signal that is caused by a wobble disk, but not for that of an RF signal distorted by a defect of a disk such as the pin hole or pin depth defect.
The conventional EFM signal detection apparatus using the envelope detection method detects peak and bottom envelopes of an RF signal, extracts a slice reference level by calculating or amplifying the detected envelopes, and slices the RF signal based on the extracted slice reference level, to generate an EFM signal. This EFM signal detection apparatus is effective in compensating for distortion of an RF signal due to a defect of a disk such as pin hole or pin depth defect. However, the EFM signal detection apparatus adopting the envelop detection method cannot effectively compensate for the distortion of an RF signal from a wobble disk.
The conventional EFM signal generating apparatus cannot accurately generate an EFM signal from a distorted RF signal in the case where a defective disk is defective due to a pin hole or pin depth defect, or where the disk is a wobble disk.
An object of the present invention is to provide an apparatus for generating an eight-to-fourteen modulation (EFM) signal of an optical disk reproducing system, capable of accurately generating the EFM signal regardless of which defects exist in an optical disk.
Another object of the present invention is to provide a method for generating an EFM signal of an optical disk reproducing system, by which an EFM signal can be accurately generated regardless of which defects exist in an optical disk.
In an aspect of the present invention, there is provided an apparatus for generating an eight-to-fourteen modulation (EFM) signal in an optical disk reproducing system, the EFM signal generated from a radio frequency (RF) signal reproduced from an optical disk. A data slicing unit selects, in response to a selection signal, (i) a first slice reference level generated by correcting the asymmetry of the RF signal, or (ii) a second slice reference signal generated using peak and bottom envelopes of the RF signal and the first slice reference level, to be a third slice reference level. The RF signal is sliced based on the third slice reference level, and the slicing result is output as the EFM signal. A selection signal generating unit generates the selection signal in response to the number of occurrences of error correction flags or EFM flags. An EFM flag generating unit generates the EFM flags in accordance with a bit pattern which is not used in demodulating the EFM signal. The error correction flags are generated in accordance with the amount of error which is present in the demodulated EFM signal.
In another aspect of the present invention, there is provided a method of generating an EFM signal from an RF signal in an optical disk reproducing system. In this aspect, the method includes: (a) continuously determining whether a first predetermined time interval has passed; (b) if the first predetermined time interval has passed, counting flags; (c) determining whether the count result is less than a first predetermined value; (d) if the count result is less than the first predetermined value, converting the RF signal into the EFM signal by slicing the RF signal based on a slice reference level which is obtained by correcting asymmetry of the RF signal; (e) if the count result is not less than the first predetermined value, continuously determining whether a second predetermined time interval has passed; (i) if the second predetermined time interval has passed, counting the flags; (g) determining whether the count value obtained in (f) is less than a second predetermined value, and if the count value is less than the second predetermined value, moving the process to (d); and (h) if the count value obtained in (f) is not less than the second predetermined value, converting the RF signal into the EFM signal by slicing the RF signal based on a slice reference level which is obtained using peak and bottom envelopes of the RF signal, wherein the flags are generated in accordance with the bit pattern which is not used in demodulating the EFM signal or the amount of error which is present in the demodulated EFM signal.